1. Field of Invention
The apparatus herein disclosed relates to apparatus and method for axial (without rotation) disconnection and/or joinder of tubular work string segments by application of fluid pressure from a remote source. Such method and apparatus have particular, but not exclusive, utility in the earth boring industry. Special utility exists for such method and apparatus when relatively flimsy tubing, such as coiled tubing, is employed in earth boring. In such boring it is frequently necessary to separate the drill string from the bottom-hole assembly in order to facilitate fishing, jarring, side-tracking or other operations. Remote connection and/or re-connection of tubular segments may be accomplished downhole, by application of fluid pressure from the surface, with the apparatus and method disclosed herein.
2. Description of Other Art
In many industrial applications there is some requirement for disconnection and joinder of tubular segments. When physical access to the separation point is convenient, and/or when application of torque on the tubulars is permissible, traditional connection/disconnection means such as threaded connections, flanged connections, hydraulic coupling and the like are frequently acceptable.
However, when access to the point of connection/disconnection is not possible, special procedures must be employed, even with threaded connections. For instance, in earth boring, the process of attempting to unscrew a threaded tubular connection at a particular point downhole is usually called "free pointing" and "backing off". That process involves complex calculations of the desired tensile force to be applied to the upper end of the drill string, balanced against the weight of the string, so that the net tensile and compressive forces at the point where the string is to be separated offset each other. If all of the threaded connections are made up of the same torque, are not damaged, and conditions are otherwise optimum, the string should un-thread at said point ("neutral point"). Too frequently, however, conditions are not optimal, and "free pointing" is not successful. Further, it cannot be used where horizontal runs of work string are to be broken.
Further, when application of torque on the tubular string is impermissible (such as when relatively flimsy tubular goods, such as coiled tubing, are used), disconnection and/or joinder has, heretofore, been even more problematic. In coiled tubing operations, a frequent cause of losing pipe in a well is a stuck bottom-hole-assembly. Jars and accelerators, which are typically used to impart a jarring force to free stuck bottom-hole-assemblies, often cannot be included in a bottom-hole-assembly because their inclusion would lengthen the bottom-hole-assembly beyond the length which a pressure lubricator could accommodate. Hence, heretofore, when a coil-tubing bottom-hole-assembly became stuck, the coil-tubing had to be severed downhole with chemical charge, jet blast or external mechanical cutters inside of an over string ("wash pipe") of pipe. After severance of the work string the remaining tubing stub was then grasped with an overshot for fishing/jarring operations. Upon being freed the bottom-hole-assembly had to then be tripped to the surface for removal of the coil-tubing stub and re-connection to the tubing string.
Pre-installation of an axial disconnect, operable by pressure from a remote (surface) precludes many of such problems. A typical axial disconnect, operated by pressure from a surface source, is the FA or FAU "Safety Hydraulic Disconnect" known in the oilfield. In such disconnects a piston of variable diameter is used to radially retain projections on flexible fingers of a first housing in annular grooves of a recess of a second housing. Upon extension of the variable diameter piston a narrowed section of the piston permits the flexible fingers to move radially inward and release. Downhole re-connection is not possible with this type of tool as the fingers are normally extended and flex radially inward only when external force is applied. Also, inadvertent disconnection can occur during heavy jarring operations and the flexible fingers are prone to failure, particularly in highly tensile operations. Further, use of a variable diameter piston, requiring a narrowed section, may impose an undesirable flow restriction in the workstring.
The invention disclosed herein represents a substantial improvement over previous disconnects in that it may be used for both disconnection and joinder of tubular segments responsive to pressure from a remote source; its main operating piston is positively locked in place against jarring forces; its latch release mechanism does not employ a narrowed piston; and, its design avoids the failure problems associated with the use of flexible metallic fingers in a highly tensile applications.